Have you ever wondered how economists keep track of the prices of goods and services over time? One way they do this is by using a measure called CPI, which stands for Consumer Price Index. CPI helps us understand how much prices have changed compared to a specific time period. In this article, we will learn how to calculate CPI so that you can understand this important economic indicator.

**Step 1: Choose a Base Year**

The first step in calculating CPI is choosing a base year. The base year is a specific year used as a reference point to compare the prices of goods and services in other years. For example, let’s say we choose the year 2020 as our base year. In 2020, the CPI is 100.

**Step 2: Collect Price Data**

Next, we need to collect price data for various goods and services. We will compare the prices of these goods and services to the prices in our base year. Let’s say we collect price data for milk, bread, and eggs.

**Step 3: Calculate the Price Change**

Now, we need to calculate the price change for each of the goods and services we’ve chosen. To do this, we divide the price in the current year by the price in the base year and then multiply by 100. For example, if a gallon of milk cost $3.50 in 2021 and $3.00 in 2020, we would calculate the price change like this:

($3.50 / $3.00) x 100 = 116.67

**Step 4: Calculate the Weighted Average**

The last step is to calculate the weighted average of the price changes for all the goods and services we’ve chosen. This means we take the price change for each item and multiply it by its weight, which is the percentage of household spending that goes toward that item. Then we add up all the weighted price changes to get the overall CPI for that year. For example, if milk has a weight of 10%, bread has a weight of 30%, and eggs have a weight of 20%, we would calculate the CPI like this:

(116.67 x 10%) + (price change for bread x 30%) + (price change for eggs x 20%) = CPI

### Conclusion:

Congratulations! You now know how to calculate CPI, an important economic indicator that helps us understand how much prices have changed over time. By following the four steps we’ve outlined, you can calculate CPI for any year you choose. Understanding CPI can help you make informed decisions about your spending and savings, and it’s an essential skill for anyone interested in economics.

So, now that you know how to calculate CPI, why not try it out for yourself? Gather some price data and see how CPI has changed over the years. Who knows, you might just discover something new and exciting about the world of economics!

## Want to Learn About Consumer Price Index for Free?

Khan Academy has hundreds of lessons for free. No ads, no subscriptions.